Threshold-dependent plant-microbe interactions shape soil microbial life-history strategies and stability across an elevational gradient

Microbial metabolic efficiency and community stability in high and low fertility soils following wheat residue addition

Microbial life-history strategies [inferred from ribosomal RNA operon (rrn) gene copy numbers] and associated genomic traits and metabolism potentials in soil significantly influence ecosystem properties and functions globally. Yet, the differences in microbial strategies and traits between disturbed (cropland) and pristine soils, along with their dominant driving factors, remain underexplored. Our large-scale survey of 153 sites, including 84 croplands and 69 pristine soils, combined with long-term field experiments demonstrates that cropland soils support microbial communities with more candidate r-strategies characterized by higher rrn copy numbers and genomic traits conducive to rapid resource utilization. Conversely, pristine soils tend to host communities aligned with more candidate K-strategies marked by high resource use potentials. Elevated nitrogen (N) and phosphorus (P) levels in cropland soils emerge as key factors promoting these candidate r-strategies, overshadowing the influence of organic carbon content, soil structure, or climatic conditions. Results from four long-term field experiments also corroborate that sustained N and P inputs significantly elevate rrn copy numbers, favoring these candidate r-strategists. Our findings highlight that land use and fertilization practices critically shape microbial life-history strategies, with nutrient availability being a decisive factor in increasing the r-strategists in cropland soils.IMPORTANCEMicrobial life-history strategies and genomic traits are key determinants shaping the response of populations to environmental impacts. In this paper, 84 cropland and 69 pristine soil samples were studied, and microorganisms in two ecosystems were categorized into two types of ecological groups using the classical copiotroph-oligotroph dichotomy, promoting a general understanding of the ecological roles of microorganisms. This study is the first to investigate the microbial life-history strategies under different land uses across five climatic zones in China. The results showed that the microbes in cropland soils are more copiotrophic than pristine soils. It also demonstrates that elevated levels of nitrogen and phosphorus in cropland soils are the key factors promoting these r-strategies. This observation emphasizes the critical role of nutrient management in shaping microbial community dynamics and ecosystem functioning and lays the foundation for predicting the response of microbial community composition under resource perturbation.

Soybean cropping patterns affect trait-based microbial strategies by changing soil properties

Do tree-based intercropping systems increase the diversity and stability of soil microbial communities?

Distribution and elevational controls on soil aggregate‐associated organic carbon (OC) and nitrogen (N) in alpine soils are not well known, but may be critical to the stabilization of soil C and N pools in alpine areas. In this study, we determined the variability in aggregate associated OC and N concentration and aggregate‐stability in 0 to 20 cm layers along the elevation gradient in an alpine forest (2,600–3,200 m) of the Qilian Mountains. The results showed that 1–2 mm macroaggregate accounted for the largest proportion (33.9%) of all aggregate fractions, and also contributed greater proportions (33.2 and 32.6%) to OC and N in bulk soils. Concentrations of OC and N, and C to N ratio increased with increasing aggregate size across all elevations. With increasing elevation, the proportion of >1 mm macroaggregates, mean weight diameter (MWD) and geometric mean diameter (GMD) increased significantly ( p < .01). Aggregate OC and N concentration and C to N ratios, and the contribution of > 1 mm aggregate OC and N to OC and N in bulk soils also increased significantly ( p < .01), while the contribution of 0.25–1 mm and 0.053–0.25 mm aggregates decreased with increasing elevation. In addition, MWD, GMD, OC and N concentration in aggregate decreased with mean annual temperature (MAT) and increased with mean annual precipitation (MAP). Our results demonstrated that the stability of soil structure improved, and accumulation of OC was mainly due to increases in the contribution of OC in the >1 mm macroaggregate with increasing elevation. Given that higher elevations in this alpine forest support large concentrations of SOC and macroaggregate OC, which may be vulnerable to climate warming.

The impoundment of the Three Gorges Reservoir (TGR) has greatly altered the hydrological regime and thus formed a distinctive riparian zone with anti-seasonal inundation and exposure, which may affect the soil aggregate properties in this riparian zone. Yet, the soil aggregate size distribution and stability influenced by the hydrological regime along the step-impounded elevation have rarely been documented. This study aimed to elucidate how the hydrological regime of the TGR affected the aggregate size distribution and stability in the riparian zone. Based on the step-impounded elevation, topsoil samples were collected from four elevation-dependent transects in a middle section of the TGR. Dry-sieving and wet-sieving methods were employed. The results showed that, with a decrease in the elevation gradient, the mass percentage of the >5 mm aggregates significantly decreased, while the proportions of the other size classes presented an increasing trend. Additionally, the mean weight diameter (MWD), geometric mean diameter (GMD), aggregate stability rate (ASR), and percentage of aggregate destruction (PAD) of the fractal dimension showed a successive decrease with a decrease in the elevation gradient, whereas PADMWD, PADGMD, PADASR, and the fractal dimension demonstrated a reverse trend. It can thus be deduced that the hydrological regime of the TGR significantly modified the aggregate size distribution and dramatically reduced the aggregate stability, which may provide a crucial basis for assessing the soil erosion in similar riparian zones.

The Water-Level-Fluctuation Zones (WLFZ) of the Lower Jinsha River, as a typical transition areas between land and water, show crucial ecological functions. However, the relationship between soil nutrients and microbial communities in different plant communities of the WLFZ is poorly understand. Therefore, we chose four typical plant communities, including Parthenium hysterophorus (P. hysterophorus), Ziziphus mauritiana (Z. mauritiana), Cynodon dactylon (C. dactylon), Zea mays (Z. mays), as a long-term plant communities experiment-monitoring site in a WLFZ of the Lower Jinsha River. By using high-throughput sequences, Mantel test and Mediation model, we explored the changing characteristics of soil nutrients and microbial communities, especially bacteria and fungi, and their driving role in the microbial stability in four typical plant communities. The results indicated that soil properties and enzyme activities noticeably changed among four types of different plant communities in the WLFZ, of which their P. hysterophorus and Z. mauritiana treatments were eventually higher than their of Z. mays and C. dactylon treatments. In the bacteria and fungi communities, the OTU number of P. hysterophorus and Z. mauritiana treatments were higher than their of C. dactylon and Z. mays treatments, which showed that the bacterial biomarkers only explained with the order, but the fungal biomarkers could explain with species. The bacterial and fungal diversity among four types of different plant communities in the WLFZ significantly changed such that the bacterial and fungal explanations of principal coordinate analysis (PCoA) was at 42.45% and 28.17%, respectively, and the anosim analysis of bacteria and fungi showed the p was 0.001 and the R was at 0.6995 and 0.7491. The bacterial and fungal co-occurrence network patterns presented that the bacterial community structure of the C. dactylon and P. hysterophorus treatments were the most complicated under the Z. mauritiana and Z. mays treatments, whereas the communities stability of C. dactylon and P. hysterophorus treatments were notably lower than that of their Z. mauritiana and Z. mays treatments. Lastly, the CCA, mantel test and intermediary analysis indicated pH served as the primary direct driver in the Z. mauritiana community, soil moisture exerted dominant effects in Z. mays and P. hysterophorus, while in C. dactylon, bacterial stability was indirectly modulated by pH mediated through SMC changes. This study highlights the major role of soil nutrients and enzyme activities in driving ecosystem stability of bacterial and fungal communities in four different plant communities in the WLFZ.

Soil microorganisms play a vital role in biogeochemical cycles by transforming plant residues into soil organic matter through catabolic processes, thereby significantly influencing carbon (C) storage. Changes in microbial metabolic limitations serve as important indicators of shifts in resource availability and microbial survival strategies. Coarse woody debris (CWD) decomposition is a stable source of C and nutrients. This process significantly affects microbial metabolism and is influenced by factors like nutrient availability, vegetation and climate. However, the effect of CWD decomposition on microbial metabolic limitations, particularly across diverse environmental gradients, remains poorly understood. Our study investigated the impact of different decay classes of CWD on soil microbial metabolic limitation along an elevational gradient in Wuyishan National Park. It examined changes in soil properties, microbial metabolic limitation and enzyme activities across the decay classes of CWD. We observed increased C limitation and decreased phosphorus (P) limitation in soil microorganisms during CWD decomposition. These trends showed consistent characteristics along the elevational gradient, with soil microbial C limitation gradually increasing and P limitation decreasing as elevation increased. This process was regulated by soil pH and oxidase activity. Our study demonstrated that the presence of CWD could modify the soil environment, allowing microorganisms to adjust their nutrient acquisition strategies, a process that would influence soil C turnover. In conclusion, resource constraints during CWD decomposition induced microbial metabolic trade‐offs and shifts in these trade‐off strategies may influence soil C storage. This study offers new insights into the interactions among plant residues, soil and microorganisms, thereby enhancing our understanding of soil C cycling in the context of global climate change. Read the free Plain Language Summary for this article on the Journal blog.

The soil microbial carbon pump (MCP) is increasingly acknowledged as being directly linked to soil organic carbon (SOC) accumulation and stability. Given the close coupling of carbon (C) and nitrogen (N) cycles and the constraints imposed by their stoichiometry on microbial growth, N addition might affect microbial growth strategies with potential consequences for necromass formation and carbon stability. However, this topic remains largely unexplored. Based on two multi-level N fertilizer experiments over 10 years in two soils with contrasting soil fertility located in the North (Cambisol, carbon-poor) and Southwest (Luvisol, carbon-rich), we hypothesized that different resource demands of microorganism elicit a trade-off in microbial growth potential (Y-strategy) and resource-acquisition (A-strategy) in response to N addition, and consequently on necromass formation and soil carbon stability. We combined measurements of necromass metrics (MCP efficacy) and soil carbon stability (chemical composition and mineral associated organic carbon) with potential changes in microbial life history strategies (assessed via soil metagenomes and enzymatic activity analyses). The contribution of microbial necromass to SOC decreased with N addition in the Cambisol, but increased in the Luvisol. Soil microbial life strategies displayed two distinct responses in two soils after N amendment: shift toward A-strategy (Cambisol) or Y-strategy (Luvisol). These divergent responses are owing to the stoichiometric imbalance between microbial demands and resource availability for C and N, which presented very distinct patterns in the two soils. The partial correlation analysis further confirmed that high N addition aggravated stoichiometric carbon demand, shifting the microbial community strategy toward resource-acquisition which reduced carbon stability in Cambisol. In contrast, the microbial Y-strategy had the positive direct effect on MCP efficacy in Luvisol, which greatly enhanced carbon stability. Such findings provide mechanistic insights into the stoichiometric regulation of MCP efficacy, and how this is mediated by site-specific trade-offs in microbial life strategies, which contribute to improving our comprehension of soil microbial C sequestration and potential optimization of agricultural N management.

Ecosystem imbalance is often associated with a feedback mechanism, which a self‐amplifying or ‐dampening process expressed by a pathway of causal processes that come back to its starting point, establishing a cycle. Warming, which is increasing worldwide due to human activities, influences the structure and functioning of ecosystems, has threatened sustainable regional and global development, especially over the mountain regions. This is because, the climatic condition rapidly changes along elevation gradients, which may amplify or mitigate the effects of climate on ecosystems. Based on it, a reference system and standardized techniques are extremely important to understand the ecosystem imbalance. Because of terrestrial oxygen production (TOP), which is the terrestrial biosphere continually absorbs CO2 and releases O2 resulting through vegetation photosynthesis, is closely related to the exchange of energy, carbon and other ecosystem factors between the atmosphere and the land. Therefore, whether TOP significantly increases indicate that accelerate in ecosystem imbalance over the Tibetan Plateau (TP) is largely unknown. To do so, integrated with characteristics and drivers of TOP, we investigated how TOP changes respond to ecosystem imbalance over the TP. These changes are influenced by related to climatic conditions, plant productivity, soil fertility, and microbial stability, which can establish a positive feedback loop that standardized direct effect is 0.99, 0.73, 0.75, and 0.75. Our findings suggest that ecosystem imbalance will accelerate with rapid TOP increase over the TP by ∼2,100. This study confirms the importance of the ecosystem imbalance under global warming in the future.

Lignite bioorganic fertilizer enhanced microbial co-occurrence network stability and plant–microbe interactions in saline-sodic soil

Intercropping increases soil macroaggregate carbon through root traits induced microbial necromass accumulation

Microbial life-history strategies and particulate organic carbon mediate formation of microbial necromass carbon and stabilization in response to biochar addition

Increased microbial complexity and stability in rhizosphere soil: A key factor for plant resilience during mining disturbance

Salt marshes are coastal wetlands that cover 2-3% of land surface area.1 These habitats carry out several essential functions such as providing habitats for many species, acting as a buffer between terrestrial land and ocean waters, and most importantly, acting as a major carbon (C) storage pool. Arbuscular mycorrhizal fungal (AMF) symbionts are key organisms in salt marsh habitats and are known to influence the following: plant zonation, plant resource competition, plant productivity, plant genetic diversity, soil C sequestration, soil C:N:P ratios, saprotrophic bacterial population and diversity, soil stability, and litter decomposition. Under rapidly changing conditions caused by climate change it is difficult to predict how AMF communities will respond to these factors, which would ultimately alter those processes. In this review, we will outline the functions and roles that AMF communities play in salt marsh soils. Additionally, we will present current knowledge and predictions of how AMF will respond to rising sea levels, elevated CO₂ levels, and eutrophication. Lastly, we will outline our research design and methods which aims to identify soil fungal diversity and abundance in different grass patches. We will also look at several factors that potentially alter soil fungi such as edge-effects, elevation gradients, patch size, soil conductivity, pH, and soil stoichiometry. Studying soil fungi is essential for understanding how these communities are predicted to react to a changing climate, and consequently alter salt marsh processes.